Magnetic control vacuum tube



July 8, 1941. c v LITTON I 2,248,712

MAGNETIC CONTROL VACUUM TUBE Filed March 20, 1940 F IG. 3.

INVENIOR. CHARLES z'KL/TTO/V B Y A TORNEY.

' tlals during certain portions of a cycle.

Patented July 8, 1941 UNITED STATES PATENT OFFICE to Mackay Radio and Telegraph ,NGI

York, N. Y a corporation of Delaware Application March :0. 1040, Serial No. 824,925

Claims. (Cl. 25047.5)

This invention relates to vacuum tube structures and more particularly to vacuum tubes wherein losses due to electrons reaching the control and are minimized.

In known vacuum tube structures the electrons emitted from a cathode are attracted to a positively biased plate or anode electrode and are controlled during this passage by a control potential applied to the grid electrode. In operation the grid may be subjected to positive potentends to direct the electrons to the grid, giving rise to grid current and consequent lowering of eillciency. For this reason the grid swing ol-an oscillator, for example, may be limited below a fixed positive value.

According to my invention I provide a mag-- netic field which tends to cause electrons to be confined to a narrow spiral path and to thus be prevented from contacting the control grid. Thus, the tube it used as an oscillator may operate with high maximum positive grid swing.

According to another feature of my invention electrons passing longitudinally between a pair of electrodes under control of a further electrode may be prevented from spreading by providing a magnetic field along the path or travel of the electron.

It is a principal object or my invention to provide a vacuum tube in which the operating emciency is improved by use of an added magnetic field.

It is a further object of my invention to provide a vacuum tube having a control electrode outside the normal path or travel of the electron stream and means for producing a magnetic field with the line of force in the direction of travel of electrons between cathode and anode.

A better understanding of. my invention, as well as other features and objects thereof will be apparent to those skilled in the art from a review or the particular description 01. my invention made in connection with the accompanying drawing, in which Figs. 1 and 2 illustrate transverse and longitudinal cross sections, respectively, or a tube embodying the principles or my invention.

Fig. 3 illustrates a transverse section or a modified form or a tube embodying features of my invention, and

Fig. 4 is a longitudinal cross-section of a further modified vacuum tube embodying further features oi. my invention.

Turning to Figs. 1 and 2, it represents an anode made 01' magnetic material and iorming a Radialiy mounted on member It are a plural ity 01 control electrode members It. These members may be in the form of sheets or plates or may be oi. wire mesh. A filamentary cathode comprising wires ll connected at one end to a ring element It and at the other end to terminals ll completes the tube element assembly. A control electrode lead It serves for supp y bias and control potential to control electrode assembly i3, it. On projecting member I4 is provided a magnetizing winding 1i, which serves to magnetize electrode members It and it to produce a magnetic field between these members. The lines of magnetic force then extend radially from member I! to anode III, as indicated by dotted lines in Fig. 1.

In operation filaments ll are brought to electron emissivity and the electrons emitted are attracted toward anode III as an average velocity dependent upon the positive bias of the anode. A control potential is supplied to grids It to vary the electron fiow'in accordance therewith. This control potential may render grid ll positive during certain portions of cycles of operation tending to divert the electrons from their normal path to said anode toward the grid elements. This diversion is prevented, or at least substantially controlled by the effect of the magnetic field existing between members it and II. when an electron attempts to move across a magnetic field, it finds a force acting upon it which tends to cause it to follow a curved path.

The radius R of curvature lor the motion of the electron is expressed in the following equation in which Ev is the measure of the electrons kinetic energy in electron volts in the plane or curvature, and H is the magnetic field strength at the point in question. The electrons are accelerated in the same direction as the magnetic field, so the initial component in a direction perpendicular to the field is quite small. For this reason the comparatively weak magnetic field is able to keep them within the confines of a very small radiuscircle. As the electrons travel away from the cathode they tend to disperse due to their mutual repulsion, causing a larger component of movement perpendicular to the magnetic field. The electrons then travel in the path of a helical spiral, which may be controlled in diameter by the magnetic field strength so that the electrons do not reach the grid.

This general principle control by the magnetic field applies to other forms oi tubes as well as that illustrated in Figs. 1 and 2.

In Fig. 3 is illustrated another form of tube using a magnetic field to control the path of travel of the electrons to the anode. In this tube the magnetic members are entirely outside the tube envelope. The anodes II, grid or control electrode member II and cathode filaments 31 are arranged within an envelope II, which may be of any desired material, glass, for example. About the tube envelope is provided a magnetic system comprising a ring oi magnetic material 32 on which are formed inwardly projecting pole pieces 33, 34. Magnetic windings 35, ll are provided on pole pieces I3, 34 to produce a magnetic field across the tube envelope ll in line with the initial electron path between filaments 31 and anodes 30.

Fig. 4 is a fragmentary view showing still another form oi. vacuum tube using a magnetic field to control the path of an electron. In this embodiment, electrons emitted from a cathode ll, which may be an indirectly heated cathode, pass longitudinally through a cylindrical control electrode H, to an anode electrode 42. Although the electrons are initially moving at a high velocity toward anode 42 they must traverse a relatively long distance through the control electrode 4| before reaching the anode. Accordingly, they tend to disperse and unless some provisions are made to prevent it many will be attracted to control electrode ii during its positive swings and will never reach the anode 42.

To prevent the electrons from reaching control electrode 4i, magnetic coil winding 43 is provided about the tube envelopes N. The magnetic field within this coil will be longitudinal thereof and consequently parallel with the normal desired path of electron flow. Because of this the electrons may be caused to follow a spiral path under control of the magnetic field and be diverted away from contact with control electrode M. If desired a shell of magnetic material may be provided about coil 43 to strengthen the magnetic field through the coil.

Although I have described a i'ew particular embodiments of my invention it should be distinctly understood that these examples serve merely as illustrations of my invention and not as limitations thereof. Many modifications withinthesoopeoimyinventionwill bereadily apparenttothoseskiliedintheart. WhatI consider to be my invention is embodied in the What I claim is:

1. A radial-type vacuum tube comprising an envelope, hollow cylindrical anode means, an electron emissive cathode within said cylindrical anode means, said anode receiving the electrons from said cathode, a control electrode disposed outside the normal path of electron fiow from said cathode to said anode for controlling the fiow oi electrons to said anode, and means for producing a magnetiefield radially with respect to said anode, said field being in the direction of said electron how and preventing diversion of said electrons from said normal path.

2. A radial-type vacuum tube comprising a tubular anode of magnetic material, means ior sealing one end of said anode, a member 0! magnetic material having an external diameter smaller than the internal diameter of said tubular anode and positioned within said anode, means tor sealing said member to said anode, both of said sealing means and at least a portion of said anode forming a chamber and at least a portion of said member being within said chamber, electron emissive means encircling said member, control electrode means disposed outside the normal path oi electron flow from said electron emissive means and said anode for controlling the flow of electrons from said emissive means to said anode. and means for producing a magnetic field between said member and said anode, said field being in the direction of said electron fiow and preventing diversion of said electrons from said normal path.

3. A vacuum tube according to claim 1 wherein said anode comprises magnetic material.

4. A vacuum tube according to claim 1, wherein said anode is of magnetic material and forms a portion 01' the envelope of said vacuum tube. said control electrode comprising a centrally disposed portion oimagneticmateriahcarrying a plurality oi radial fins, said cathode being arranged between said centrally disposed portion and said anode, and further comprising means for applying a magnetizing force to said anode and said centrally disposed member.

5. A vacuum tube according to claim 1, wherein said control electrode comprises a plurality of radially positioned vanes.

CHARLES V. LI'ITON. 

